pgsql: Fix arrays comparison in CompareOpclassOptions()

Fix arrays comparison in CompareOpclassOptions()

The current code calls array_eq() and does not provide FmgrInfo. This commit
provides initialization of FmgrInfo and uses C collation as the safe option
for text comparison because we don't know anything about the semantics of
opclass options.

Backpatch to 13, where opclass options were introduced.

Reported-by: Nicolas Maus
Discussion: https://postgr.es/m/18692-72ea398df3ec6712%40postgresql.org
Backpatch-through: 13

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a6fa869cfa4e8f0226f22f717f5b0aa5eed60588

Modified Files
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contrib/pg_trgm/expected/pg_trgm.out | 3 +++
contrib/pg_trgm/sql/pg_trgm.sql | 4 ++++
src/backend/commands/indexcmds.c | 11 +++++++++--
3 files changed, 16 insertions(+), 2 deletions(-)